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author | chriseth <c@ethdev.com> | 2015-06-01 18:32:59 +0800 |
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committer | chriseth <c@ethdev.com> | 2015-06-05 23:34:26 +0800 |
commit | 88096c2c694983da327fd0fc46c31dc6f7404f73 (patch) | |
tree | fb84765bb8ab726354bf9c4d44d152008ec2c530 /ConstantOptimiser.h | |
parent | d309c3c76827606c4cabd5660035df394a16b601 (diff) | |
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Compute constants
Diffstat (limited to 'ConstantOptimiser.h')
-rw-r--r-- | ConstantOptimiser.h | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/ConstantOptimiser.h b/ConstantOptimiser.h new file mode 100644 index 00000000..e75eff38 --- /dev/null +++ b/ConstantOptimiser.h @@ -0,0 +1,147 @@ +/* + This file is part of cpp-ethereum. + + cpp-ethereum is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation, either version 3 of the License, or + (at your option) any later version. + + cpp-ethereum is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with cpp-ethereum. If not, see <http://www.gnu.org/licenses/>. +*/ +/** @file ConstantOptimiser.cpp + * @author Christian <c@ethdev.com> + * @date 2015 + */ + +#pragma once + +#include <vector> +#include <libdevcore/CommonData.h> +#include <libdevcore/CommonIO.h> + +namespace dev +{ +namespace eth +{ + +class AssemblyItem; +using AssemblyItems = std::vector<AssemblyItem>; +class Assembly; + +/** + * Abstract base class for one way to change how constants are represented in the code. + */ +class ConstantOptimisationMethod +{ +public: + /// Tries to optimised how constants are represented in the source code and modifies + /// @a _assembly and its @a _items. + /// @returns zero if no optimisations could be performed. + static unsigned optimiseConstants( + bool _isCreation, + size_t _runs, + Assembly& _assembly, + AssemblyItems& _items + ); + + struct Params + { + bool isCreation; ///< Whether this is called during contract creation or runtime. + size_t runs; ///< Estimated number of calls per opcode oven the lifetime of the contract. + size_t multiplicity; ///< Number of times the constant appears in the code. + }; + + explicit ConstantOptimisationMethod(Params const& _params, u256 const& _value): + m_params(_params), m_value(_value) {} + virtual bigint gasNeeded() = 0; + virtual void execute(Assembly& _assembly, AssemblyItems& _items) = 0; + +protected: + size_t dataSize() const { return std::max<size_t>(1, dev::bytesRequired(m_value)); } + + /// @returns the run gas for the given items ignoring special gas costs + static bigint simpleRunGas(AssemblyItems const& _items); + /// @returns the gas needed to store the given data literally + bigint dataGas(bytes const& _data) const; + /// @returns the gas needed to store the value literally + bigint dataGas() const { return dataGas(toCompactBigEndian(m_value, 1)); } + static size_t bytesRequired(AssemblyItems const& _items); + /// @returns the combined estimated gas usage taking @a m_params into account. + bigint combineGas( + bigint const& _runGas, + bigint const& _repeatedDataGas, + bigint const& _uniqueDataGas + ) + { + // _runGas is not multiplied by _multiplicity because the runs are "per opcode" + return m_params.runs * _runGas + m_params.multiplicity * _repeatedDataGas + _uniqueDataGas; + } + + /// Replaces the constant by the code given in @a _replacement. + void replaceConstants(AssemblyItems& _items, AssemblyItems const& _replacement) const; + + Params m_params; + u256 const& m_value; +}; + +/** + * Optimisation method that pushes the constant to the stack literally. This is the default method, + * i.e. executing it does not alter the Assembly. + */ +class LiteralMethod: public ConstantOptimisationMethod +{ +public: + explicit LiteralMethod(Params const& _params, u256 const& _value): + ConstantOptimisationMethod(_params, _value) {} + virtual bigint gasNeeded() override; + virtual void execute(Assembly&, AssemblyItems&) override {} +}; + +/** + * Method that stores the data in the .data section of the code and copies it to the stack. + */ +class CodeCopyMethod: public ConstantOptimisationMethod +{ +public: + explicit CodeCopyMethod(Params const& _params, u256 const& _value); + virtual bigint gasNeeded() override; + virtual void execute(Assembly& _assembly, AssemblyItems& _items) override; + +protected: + AssemblyItems m_copyRoutine; +}; + +/** + * Method that tries to compute the constant. + */ +class ComputeMethod: public ConstantOptimisationMethod +{ +public: + explicit ComputeMethod(Params const& _params, u256 const& _value): + ConstantOptimisationMethod(_params, _value) + { + m_routine = findRepresentation(m_value); + } + + virtual bigint gasNeeded() override { return gasNeeded(m_routine); } + virtual void execute(Assembly&, AssemblyItems& _items) override + { + replaceConstants(_items, m_routine); + } + +protected: + /// Tries to recursively find a way to compute @a _value. + AssemblyItems findRepresentation(u256 const& _value); + bigint gasNeeded(AssemblyItems const& _routine); + + AssemblyItems m_routine; +}; + +} +} |